1. Field of the Invention
The present invention relates to an ink composition, and more particularly to a highly bleed-alleviating ink composition and its application in ink-jet printing.
2. Background of the Invention
Ink-jet printing technology has been developed for many years. The advantages include low price, low noise, and good full-color printing quality. Also, various substrates recording substrate including plain paper, paper for special printing, and transparency can be printed upon.
Ink-jet printing is a non-contact method that involves ejecting ink droplets onto a recording substrate. For color ink-jet printing, preferable ink must meet the following requirements:                (1) Ink printed on the recording substrate has no feathering or bleeding.        (2) Ink printed on the recording substrate dries very fast.        (3) After printing, the printing nozzles do not generate clogging.        (4) The ink used must have good storage stability.        (5) The ink used must be non-toxic for safety.        
Bleeding is always a problem in ink-jet printing. When ink of one color is printed on paper, if the ink droplets can not effectively coagulate, they will, by means of capillarity action through the paper fibers, diffuse into another color. This phenomenon is called bleeding, and severely affects printing quality.
Several methods have been proposed to reduce bleeding. The first and most frequently-used method is to increase the distance between various droplets. This method also greatly decreases the resolution. The second method is to lengthen the time interval between every two ink droplets. In U.S. Pat. No. 5,371,531, two types of ink with different drying rate are used. The ink droplets of the first type are first ejected. The ink droplets of the second type are then ejected after the ink droplets of the first type have dried. However, the printing rate is limited. The third method is to add a zwitterionic or non-ionic surfactant to ink. When the surfactant is added in a concentration equal to or above its critical micelle concentration, bleeding can be alleviated.
Until now, the most effective method to alleviate bleeding of ink on the recording substrate has been developing in adding an effective amount of surfactant. By changing the physical property of the ink, such as surface tension or viscosity, to achieve bleed-alleviation of the ink droplets.